In wideband CDMA and other wireless mobile communications systems, the wireless signal may not take a direct path between the transmitter and receiver. A wireless signal may be propagated and received through multiple paths or rays. The multiple paths are due to reflections and diffractions of the wireless signal. The transmission of the wireless signals across these multiple reflective paths is often referred to as multi-path propagation.
The multi-path effect often results in delayed or advanced versions of the signal being received, and also results in fluctuations in the amplitude and phase in these versions of the received signal. The range of delays between different versions of the same signal received along different paths is referred to as the multi-path delay spread.